Systems for the transformation of other types of energy (e.g., hydro, steam, etc.) into electrical energy, and the transmission of this electrical energy to the point of consumption may be referred to generally as electric power systems. Alternating current (AC) is generally used in modern power systems, because it may be easily converted to higher or lower voltages by means of transformers thereby enabling each stage of the electric power system to be operated at an appropriate voltage.
The frequency of electric power supply in the United States is 60 hertz (cycles per second). In other parts of the world, for example the United Kingdom, the power supply is 50 hertz. The frequency of a system is dependent entirely upon the speed at which the supply generator is rotated by its prime mover. Hence frequency control is basically a matter of speed control of the machines in the generating stations. Modern speed-control is very effective and hold frequency almost constant; deviations are seldom greater than 0.02 hertz.
In an AC system the voltage continually varies with time, at one instant being positive and a short time later being negative, going through 60 complete cycles of change in each second. Ideally a plot of the time change should be a sine wave. In a poorly designed generating equipment, or a poorly designed load such as a variable speed heat pump, harmonics may be present and the wave shape may resemble a sine wave but have erratic looking fluctuations in the wave print.
Practically all major power equipment is supplied by three-phase circuits. Three-phase circuits are essentially three single-phase circuits each of which has its own sine wave voltage. If phase balance is perfect, each of the three voltages is of the same magnitude but displaced in time from the others by one-third cycle. Modern three phase generators are designed to have almost perfect phase balance.
A typical electric power system consists of several principle elements including: the power station; a set of transformers to raise the generated power to the high voltages used on the transmission lines; the transmission lines; the substations at which the power is stepped down to the voltage on the sub-transmission lines; the sub-transmission lines; and the transformers that lower the sub-transmission voltage to the level used by the consumer's equipment.
In a typical system, the generators at the central power station typically deliver a voltage of from 1,000 to 26,000 volts (V). Higher voltages are usually undesirable because of difficulties of insulation and the danger of electrical breakdown and damage. This voltage is stepped up by means of transformers to values ranging from 138,000 V (138 Kilovolts or "KV") to 765,000 V (765 KV) for the primary transmission line (the greater the voltage on the line, the less the current and consequently the less the power loss, the loss being proportional to the square of the current).
At the substation, the voltage may be transformed down to levels of 69 KV to 138 KV for further transfer on the sub-transmission system to yet another set of transformers which steps the voltage down to a distribution level such as 2.4, 4.2, 15, 27 or 33 Kilovolts (KV). Finally, the voltage is transformed once again at the distribution transformer near the point of use to 240 V to 120 V (i.e., 110 volt household voltage). Thus, the central station of a power system consists of a prime mover, such as a water or steam terminal, which operates an electric generator.
A key component of the overall system, in order to transmit the power generated at the system to the end user or consumer, is the high voltage transmission line or sub-transmission line. The lines of high voltage transmission systems are usually composed of wires of copper, aluminum, copper clad or aluminum clad steel, and galvanized steel, which are suspended from a tall lattice work tower of steel by strings of porcelain insulators. By the use of clad steel wires and high towers, the distance between towers can be increased, and the cost of the transmission line thus reduced. In modern installations with essentially straight paths, high voltage lines may be built with, for example, as few as four towers to the mile (e.g., a 765 KV lines). In some areas, high voltage lines are suspended from tall wooden poles spaced more closely together. For lower voltage sub-transmission and distribution lines, wooden poles are generally preferred rather than steel towers.
Long transmission lines have considerable inductance and capacitance as well as resistance. When a current flows through the lines, inductance and capacitance have the effect of carrying the voltage on the line as the current varies. Thus, the supply voltage varies with the load. Several kinds of devices are used to overcome this undesirable variation, in an operation called regulation of the voltage. The concept of electrical induction discovered by British Physicist Michael Faraday has been defined as the creation of an electric current in a conductor moving across a magnetic field. A similar, but inverse concept is the concept of reluctance.
Reluctance is the opposition offered in a magnetic circuit to a magnetic flux, but more specifically, is the ratio of the magnetic potential difference to the corresponding flux. Thus, a change in the conductor density, material, or other factors would affect the induction of electricity as well as present a reluctance change with respect to the aforementioned transmission and sub-transmission lines of an electrical power system.
The art to which the invention relates includes an apparatus and method of detecting galvanization loss on steel conductors or steel components of conductors. Such an overhead line galvanization detector has been referred to as a corrosion detector which is actually a misnomer because galvanization loss is believed to by some to merely mark the beginning of a corrosion cycle. In actuality, however, it has been shown that galvanization of steel members used in a water or other corrosive environments (e.g., considering the galvanic cell conditions created by water and metallic conductor components) has little if any effect as a corrosion retardant. One such device for detecting galvanization loss is a device called an "Overhead Line Corrosion Detector" marketed by Cormon LTD. of West Sussex in the United Kingdom.
The Cormon device and method of detecting galvanization loss includes an apparatus configured to rest on, engage, and travel along a transmission line or overhead conductor. The Cormon device incorporates a first drive component referred to as a "tug" coupled to a data transmission unit. Both units are designed to be powered by rechargeable batteries. A detector head is coupled or linked to the data transmission unit and is pulled along with the assembly by the tug.
The tug component, therefore, serves merely as the motive force to pull the detection components along the length of the conductor (i.e., the data collection unit and the cylindrical collar-like detector head are moved along the conductor by the motorized tug). A transmitter is associated with the data collection unit and is believed to employ an RF data carrier signal to send the data collected by the detector head to a ground station or central processing unit (CPU).
The detector head or sensing head as it is referred to by Cormon is a hollow cylinder which clamps around the conductor. It contains a field winding and a pickup coil. When high frequency current is passed through the field winding, it generates a magnetic field surrounding the conductor. The magnetic field surrounding the conductor penetrates the conductor and induces eddy currents around the individual strands as the sensing head is pulled along the conductor.
The alternating flux induces a voltage in the pickup coil which is processed to give an in phase and quadrature output voltage, the magnitudes of which depend on the quality of the galvanized layer. Thus, the voltage differences realized by the pickup coil are attributable to the eddy currents induced within conductor as the sensing head is moved along the conductor. The detected voltage differences are correlated to the loss of galvanization through a series of algorithms, the manipulation of which is carried out by the CPU.
It is known that the Cormon device does not detect loss of cross-sectional area of steel reinforcing members of overhead conductors despite the name given the device by Cormon.
Considering the useful life of an overhead conductor is believed to be within the range of 10-80 years, and considering that many of the steel reinforced overhead conductors found in the United States, and many other countries of the world, were put in service in the 1930's and 1940's, it is particularly important to be able to determine the remaining useful life of such conductors. In addition, considering the extraordinary high cost of replacing such conductors and the attendant liability associated with energized conductor failure (i.e., conductors falling from their towers) it would be advantageous to invent a device capable of detecting the loss of cross-sectional area of steel reinforcing members of a conductor in a power transmission or sub-transmission line attributable to corrosion of the steel members. The reliability of the power system would be greatly enhanced if the near failures could be replaced before failure.
Canadian Patent Number 921556, incorporated by reference as if fully set forth herein is directed to a method and associated apparatus for the electrical detection of flaws in materials. The Canadian device incorporates a plurality of current carrying coils which are placed beside the material to be tested. Some of the coils are then energized, and the resultant effect is detected by a pick up coil. The Canadian device differs significantly in structure and function from the apparatus and method of the present invention.
U.S. Pat. No. 4,218,651 granted to Ivy, incorporated by reference as if fully set forth herein, is directed to an apparatus for detecting longitudinal and transverse imperfections in elongated ferrous work pieces. The Ivy device differs significantly in structure and function from the apparatus and method of the present invention.
U.S. Pat. No. 2,897,438 granted to Fearon, incorporated by reference as if fully set forth herein, is directed to a casing joint detector. The Fearon invention is similar to the Ivy and Canadian devices, and it too differs significantly in structure and function from the apparatus and method the present invention.
Accordingly, until now, there is no known method to measure the loss of cross-sectional area of steel reinforcing members of a conductor in a power transmission or sub-transmission line attributable to corrosion of the steel members.